Preheat the oven to 400°F.
Make the dressing. In a small bowl, whisk together the minced shallot, mustard, lemon juice, sherry vinegar, salt, pepper, and olive oil. Set aside.
Cut the potatoes into halves and transfer them to a large baking sheet. If some of the potatoes are particularly large, cut them into quarters. Toss the potatoes with 1 ½ tablespoons of the olive oil, za’atar, salt, and pepper. Slide the potatoes into the oven and set a timer for 40 minutes.
While the potatoes are roasting, bring a medium saucepan of water to a boil over medium-high heat. Add the lentils to the saucepan and simmer until just tender, about 18-20 minutes. Drain the lentils and transfer to a bowl. Toss the warm lentils with 2 tablespoons of the dressing, some salt and pepper, and set aside.
Separate the ramp leaves from the stems. Mince the ramp leaves and set aside. Finely chop ramp stems.
Once the 40 minute timer on the potatoes rings, take the potatoes out of the oven and give them a stir. Push them over to one side of the baking sheet. Drop the asparagus and chopped ramp stems on the empty part of the baking sheet. Toss the asparagus/ramp stems with the remaining olive oil, salt and pepper. Slide the baking sheet back into the oven for 10 minutes, or until asparagus is bright green and tender.
To serve, combine the potatoes, asparagus/ramp stems, lentils, ramp leaves, radishes, dill, and remaining vinaigrette in a large bowl. Season the salad with salt and pepper, and toss to combine. Serve immediately.